Duncan A J, Elwert C, Villalba J J, Yearsley J, Gordon I J
The Macaulay Institute, Craigiebuckler, Aberdeen, UK.
Oecologia. 2007 Sep;153(3):617-24. doi: 10.1007/s00442-007-0771-6. Epub 2007 Jun 5.
Ruminant herbivores have been shown to learn about food properties by associating food flavours with the food's post-ingestive consequences. Previous experimentation supporting the conditioned food aversion/preference hypothesis has generally employed very simple diet learning tasks which do not effectively represent the wide range of foods selected within single bouts typical of wild, free-ranging ruminant herbivores. We tested the ability of a ruminant herbivore to associate a food with artificially administered nutrient rewards in a designed experiment where we altered the temporal pattern of encounter with the food as well as the nature (fast or slow reward) of the post-ingestive outcome. Twenty-four goats were offered branches of Sitka spruce (SS) and Norway spruce (NS) for 4 h per day on two days per week for five weeks. The pattern of feeding varied with treatment such that the species on offer changed every hour (short) or every 2 h (long). The energy treatment altered the reward delivered during Sitka consumption so that animals were dosed either with predominantly sugar (rapidly fermented), predominantly starch (slower fermentation rate), or with water (placebo). Preference was measured on the day following each learning day. We expected that goats would find it easier to associate SS with post-ingestive rewards when the duration of encounter was longest, and that associations would be stronger with the most rapidly digested post-ingestive reward. In the event, goats did not alter their consumption of SS in response to the treatments. Our results suggest that at the scale of temporal resolution of encounters with different plant species (1-2 h), and at the different rates of experiencing post-ingestive consequences tested in this experiment, ruminants do not appear to discriminate the nutritive properties of foods predominantly through a post-ingestive feedback mechanism. They must, instead, use a range of cues-including post-ingestive consequences-to assess food properties.
反刍食草动物已被证明可通过将食物味道与食物摄入后的后果联系起来，从而了解食物特性。先前支持条件性食物厌恶/偏好假说的实验通常采用非常简单的饮食学习任务，这些任务无法有效代表野生、自由放养的反刍食草动物单次采食中所选择的广泛食物种类。在一项设计实验中，我们改变了与食物接触的时间模式以及摄入后结果的性质（快速或缓慢奖励），以此测试反刍食草动物将食物与人工给予的营养奖励联系起来的能力。每周两天，连续五周，每天给24只山羊提供4小时的锡特卡云杉（SS）和挪威云杉（NS）树枝。喂食模式因处理方式而异，使得提供的树种每小时（短）或每2小时（长）更换一次。能量处理改变了锡特卡云杉采食期间给予的奖励，使动物要么主要摄入糖（快速发酵），要么主要摄入淀粉（发酵速度较慢），要么摄入水（安慰剂）。在每个学习日之后的那天测量偏好。我们预计，当接触时间最长时，山羊会更容易将锡特卡云杉与摄入后奖励联系起来，并且与消化最快的摄入后奖励的联系会更强。结果，山羊并未因处理方式而改变对锡特卡云杉的采食。我们的结果表明，在与不同植物物种接触的时间分辨率尺度（1 - 2小时）以及本实验中测试的不同摄入后结果体验速率下，反刍动物似乎并未主要通过摄入后反馈机制来区分食物的营养特性。相反，它们必须使用一系列线索——包括摄入后结果——来评估食物特性。
